1. Field of the Invention
The present invention relates to a cast-in-place concrete pile and a method of constructing the same in the ground.
2. Description of Prior Art
Heretofore, a cast-in-place concrete pile has been constructed by excavating the ground, inserting steel bars into thus excavated hole over the full length of the excavated hole, and then casting concrete into the excavated hole. However, recently a cast-in-place concrete long pile having the length of about 50 m to 60 m is required at a filled up land and the others. In such case, it takes a long time period and considerable labor for inserting the steel bars over the full length of the excavated hole. Utility Model Unexamined Publication No. 02-97426 proposes a cast-in-place concrete pile consisting of a steel fiber mixed lower concrete layer and a reinforced upper concrete layer including the steel bars. The concrete pile is designed such that the formation of cracks in the lower part of the concrete pile is prevented by the mixed lower concrete layer. On the other hand, a bending stress and a shear force occurring from, for example, an earthquake, a strong wind, etc., are borne by the reinforced upper concrete layer. And besides, as the steel bars are included only in the reinforced upper concrete layer, working hours and labor necessary for inserting the steel bars into the excavated hole can be reduced. The prior art written in the Utility Model Unexamined Publication No. 2-97426 describes about a method of constructing the cast-in-place concrete piles in the ground. That is, the excavated hole is formed in the ground. Concrete including steel fibers is cast into the bottom of the excavated hole, and then placing the steel bars on the thus cast concrete in the excavated hole. Subsequently, concrete is cast into the excavated hole to form the reinforced upper concrete layer on the mixed lower concrete layer. However, since the lower portions of the steel bars are not embedded into the mixed lower concrete layer, the bonding strength between the mixed lower concrete layer and the reinforced upper concrete layer is not enough to integrate the concrete pile in one-piece. Moreover, since the specific gravity of iron of the steel fibers, which is about 7.8, is much larger than that of an aggregate such as pebbles or sand, etc., which is about 2.7, the steel fibers are apt to sink toward to the bottom of the excavated hole as compared with the aggregate until the concrete including the steel fibers is hardened. As a result, it may be not expected that the steel fibers are uniformly dispersed in the mixed lower concrete layer. That is, the steel fibers are densely distributed to the lower side of the mixed lower concrete layer and sparsely distributed to the upper side of the mixed lower concrete layer. Therefore, there is a possibility that the upper side of the mixed lower concrete layer does not have a designed strength thereof. Consequently, there are serious problems with respect to the strength of the upper side of the mixed lower concrete layer and the bonding strength between the mixed lower concrete layer and the reinforced upper concrete layer. On the other hand, when fluidity of the concrete including the steel fibers is lowered, the sinking of the steel fibers having the high specific gravity is prevented to some extent. However, if the fluidity of the concrete including the steel fibers is lowered excessively, it is so difficult to cast the concrete with tremie tube into the bottom of the excavated hole having the depth of 50 m to 60 m.